1. Division of Family Medicine, Taoyuan Armed Forces General Hospital, Taoyuan 325, Taiwan
2. Graduate Institute of Medical Sciences, National Defense Medical Center, Taipei 114, Taiwan
3. School of Public Health, National Defense Medical Center, Taipei 114, Taiwan
4. Institute of Labor, Occupational Safety and Health, Ministry of Labor, New Taipei City 221, Taiwan
5. School of Respiratory Therapy, College of Medicine, Taipei Medical University, Taipei 110, Taiwan